The present invention relates to an exhaust gas recirculation system for controlling the flow of exhaust gas from an exhaust manifold to an intake manifold of an internal combustion engine, and more particularly, to an improved actuator and control assembly for such an exhaust gas recirculation system.
Although the use of the present invention is not limited to any particular type or configuration of engine, its use is especially advantageous in connection with a heavy duty diesel engine, for reasons which will become apparent subsequently, and the invention will be described in connection therewith.
Typically, exhaust gas recirculation (EGR) valves have been disposed between the engine exhaust manifold and the engine intake manifold, and have been operable, when in the open position, to permit the recirculation of exhaust gas from the exhaust side of the engine back to the intake side. As is well known to those skilled in the art, such recirculation of exhaust gasses is helpful in reducing various engine emissions.
An EGR system including an electrically operated type actuator is illustrated and described in U.S. Pat. No. 5,606,957. The actuator for the valve stem in the cited patent is a stepper motor, which is generally satisfactory in performing the basic function of opening and closing the EGR valve, but does have a number of performance limitations. Another type of electrically operated actuator is illustrated and described in copending application U.S. Ser. No. 09/249,715, filed Feb. 12, 1999 in the names of Michael J. Sitar, David W. Deppe and Bill D. Wood, for an "EGR SYSTEM AND IMPROVED ACTUATOR THEREFOR", which is assigned to the assignee of the present invention and incorporated herein by reference. In the device of the above-incorporated application, the actuator includes an electric motor of the relatively high-speed, continuously rotating type, such as a permanent magnet DC commutator motor. The actuator also includes a reduction gear train, suitable to convert the output of the motor into a motion of the valve member which satisfies the operating requirements, in terms of the speed of movement of the valve member versus the force applied to the valve member, at any given position of the valve member during its opening and closing cycle.
In the case of either of the devices referred to above, there is a need for electrical/electronic controls, to control the opening and closing of the EGR valve, in response to variations in any one of a number of different engine operating conditions. Those skilled in the vehicle and engine arts understand that, at least in general, it is desirable for such controls to be integrated with the EGR valve and actuator assembly. If the controls are integrated into the actuator assembly, the required wiring harness is simplified, and the connection to the actuator motor and the position sensor can be internal to the actuator housing, thus protecting these connections from environmental problems. In some vehicle applications, there is simply not enough room available in the vehicle engine control module (ECU) to add the necessary control circuitry.
As is also well known to those skilled in the art, when dealing with a heavy duty diesel engine, and its various auxiliary components, temperature and the effects of various corrosive materials which are present must also be taken into account in designing and locating the various auxiliary components. Excessive temperatures can negatively effect performance of many components, and corrosive materials can negatively impact the life of the components.
It has been determined that when an EGR valve is located on the intake manifold side of a diesel engine, various pollutants in the exhaust gas have the opportunity to condense out of the stream of exhaust gas, because the intake manifold side of the engine is relatively cooler than the exhaust manifold side. The pollutants which condense out of the exhaust gas are of a type which tend to corrode the EGR valve and valve seat combination, as well as other system elements, such as the EGR cooler and associated pipes and plumbing. Thus, it has been determined that the EGR valve itself has better durability if it is located on the exhaust manifold side of the engine.
As was noted previously, it is desirable for the electronic controls associated with the EGR valve actuator to be integral with the EGR valve assembly. Unfortunately, if the EGR valve assembly is located on the exhaust manifold side of the engine, for the reasons discussed above, the electronic controls associated with the EGR valve actuator can no longer use the relatively inexpensive, commonly available electronic components which are typically rated for continuous operation at 125.degree. Centigrade. Instead, having the EGR valve assembly on the exhaust manifold side of the engine would require electronic components which are rated for continuous operation at up to 400.degree. Centigrade. Such components are either not yet readily available commercially, or if available, are extremely expensive.